The invention relates to fluid handling apparatus and more particularly to apparatus for aspirating a selected quantity of fluid into a pipet or other similar vessel and for discharging the fluid from the pipet.
Recently there has been increased emphasis on safety in the laboratory, particularly with regards to pipetting biological fluid specimens. A wide variety of hand-held, manually-operated syringes have been developed to provide safe collection and discharge of such fluids. However, the known conventional syringes are relatively tedious to operate because the plungers or pistons therein must be manually pulled and pushed for each pipetting operation, thus causing considerable fatigue after many repetitions. Also the devices are relatively bulky, especially those which are capable of pipetting from 1 to 10 milliliters or more of fluid. In particular, since the conventional syringe is coaxially mounted over the upper end of a pipet, the overall length of such a pipetting device (with pipet attached) is not suitable for operation in restricted areas, such as under laminar flow or biological containment hoods used in medical laboratories. Moreover, some of the devices require cleaning of elements thereof to avoid cross-contamination of successively pipetted fluids.
Another type of pipetting device uses a bulb aspirator to siphon fluid into an attached pipet. A major problem associated with this type of pipettor is that the pipet cannot be charged with a precise volume of fluid in one operation; but, as in conventional mouth pipetting, the pipette is filled above the desired volume and the excess fluid is then discharged until the meniscus at the upper surface of the fluid has dropped to a selected mark on the outer surface of the pipet body. Not only is this a time consuming procedure, but also it is difficult to achieve a high level of accuracy. It is obvious that the accuracy of such a technique is not only dependent on the skill of the operator but also on the volumetric accuracy of the graduated pipet used therewith. Also, this technique requires discharging of the excess fluid into the atmosphere above the fluid sample; and thus the risk of spreading contaminated or toxic fluid into the atmosphere is increased.
Finally, another type of dispenser has been more recently developed to utilize separate sources of vacuum and pressure to completely charge and discharge a pipet. Such a device is shown in Canadian Pat. No. 938,594. A shortcoming of the dispenser is that the volume of fluid to be transferred is determined only by the total capacity of the pipet utilized. Also, this type of pipettor requires washing of the tubing and valving means therein between collections of different fluids in order to prevent cross-contamination of different fluid specimens. Furthermore, the hand-held pipet-operating subassembly of this type of fluid handling apparatus is relatively bulky and difficult to use in restricted areas.
Accordingly, a major object of the present invention is to provide an apparatus for collecting and dispensing fluids which overcomes the aforementioned problems or shortcomings.
Also it is an object of this invention to provide a pipetting apparatus adapted to charge a pipet with a precise amount of liquid and to discharge the liquid at a metered rate, wherein neither the volumetric precision nor rate of discharge of the pipetting device depends solely on the dimensional characteristics of the pipet or liquid-retaining vessel used therewith.
It is a further object of this invention to provide a versatile pipetting device having volumetric adjusting means which permit the selection of volumes in the microliter or macroliter range, or in both ranges. Another object is to furnish a pipetting device which can be easily and accurately calibrated to compensate for changes in barometric pressure exerted on the fluid to be pipetted. Also, another object is to provide a pipetting apparatus which may be adjusted to collect and dispense any increment of volume less than the total available volume of the pipet employed therewith.